Arc Flash Warning Labels – What Do They Mean?

Understand Arc Flash Hazard labels and PPE requirements

The NFPA 70E – includes several requirements related to arc flash and energized work.
  • Appropriate safety-related work practices shall be determined before any person approaches exposed live parts within the Limited Approach Boundary by using both shock hazard analysis and flash hazard analysis.

  • A flash hazard analysis shall be done in order to protect personnel from the possibility of being injured by an arc flash. The analysis shall determine the Flash Protection Boundary and the personal protective equipment that people within the Flash Protection Boundary shall use.

  • The incident energy exposure level shall be based on the working distance of the employee’s face and chest areas from a prospective arc source for the specific task to be performed.

 
The NFPA 70E standard provides 5 Arc Rating levels of PPE
  • Class 0 for incident energy up to 1.2 cal/cm2

  • Class 1 for incident energy up to 4 cal/cm2

  • Class 2 for incident energy up to 8 cal/cm2

  • Class 3 for incident energy up to 25 cal/cm2

  • Class 4 for incident energy up to 40 cal/cm2

Definitions
  • Arc Flash Boundary (outer boundary): The flash boundary is the farthest established boundary from the energy source. If an arc flash occurred, this boundary is where an employee would be exposed to a curable second-degree burn (1.2 calories/cm2). The issue here is the heat generated from a flash that results in burns.

  • Limited Approach Boundary - A shock protection boundary not to be crossed by unqualified persons unless escorted by a qualified person.

  • Restricted Approach Boundary - A shock protection boundary to be crossed by only qualified persons. When crossed the use of shock protection techniques and equipment is required.

  • Prohibited Approach Boundary - A shock protection boundary only to be crossed by qualified persons. When crossed the same protection is required as if direct contact is made with the live part.

  • Flash Protection Boundary - Distance at which the incident energy level equals 1.2 cal/cm2 for fault clearing time greater than 0.1 seconds. For voltages greater than 1000V, use 1.5 cal/cm2 for clearing times that are 0.1 seconds or faster.

Personal protective equipment (PPE)

is required to limit worker’s exposure to incident energy should an incident occur. Incident energy causes burns, which are the major hazard to individuals from an arc flash. As a benchmark, 1.2 cal/cm2 is the energy at which a 2nd degree burn will occur. At 3 cal/cm2 a light weight cotton shirt may ignite. One layer of flame-retardant material typically provides protection up to 4 cal/cm2. Three layers of flame-retardant material typically provide protection up to 25 cal/cm2. The PPE should be based on the highest expected incident energy from the calculations.

 

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